| Spirulina platensis,one of the main kinds of microalgae which have to date realized mass cultivation,contains high content of high quality proteins and bioactive substances,and has important application potentials in food,feedstock,cosmetics industries et al.However,the big problem exists in Spirulina production process is the large consumption of water resources,i.e.about 1000～2000 ton water for 1 ton Spirulina production.The main reason for culture medium’s difficulty to be reutilized is the excretion of auto-growth inhibitors during S.platensis’s growing process.We researched on the autoinhibitor and the main results were listed as below:A long-term reused culture medium of Spirulina platensis was tested for the effect on the growth of itself.The reused culture medium was appended nutrient salt as well as Zarrouk culture.The cultures were inoculated with new cells and incubated under the same conditions.In order to know why the usd culture medium affected the growth of Spirulina platensis itself,cell density,soluble phosphate concentration,nitrate concentration and the content of chlorophyll,carbohydrate and protein were measured during the experiment.The different molecular weight distributions of the reused culture medium were separated with 100 kDa,10 kDa,5 kDa and 1 kDa membrane and the components of the inhibitor was analyzed.Although nutrition was complemented enough,the results showed that long-term reused culture medium inhibited the cell growth of Spirulina platensis,we found the the specific growth rate of reused medium decreased by 23%,and the absorption of nitrate and phosphate was decrease 36%and 37%,respectively,compare with the fresh culture medium.Data demonstrated that the nitrogen metabolism,phosphorus metabolism and the synthesis of intracellular proteins and chlorophyll of Spirulina platensis were all destroyed.Additionally,the intracellular proteins content and chlorophyll were 85 percent and 65 percent of the fresh culture medium,respectively.The auto-growth inhibitor of Spirulina platensis were extracellular polysaccharide and their molecular weights are over 100 kDa.The Extracellular polysaccharide of Spirulina were isolated and purified with DEAE Sepharose ion-exchange column chromatography and Sephacryl S-400 column chromatography repeatedly.Three water-soluble homogeneous polysaccharides(EPS 1-1,EPS 1-2 and EPS2-1)were obtained.260nm and 280nm can not be detected by UV scanning.It indicated that there are no nucleic acid and protein in these components.The molecular weights of EPS were determined by HPLC.A single and symmetrically sharp peak was found by size exclusion column,It indicated that they were homogeneous polysaccharide.According to the calibration molecular curve of the elution times of standards,the molecular weights of EPS1-1、EPS1-2 and EPS2-1 were estimated to be more than 1100 kDa、413 kDa and 114 kDa,respectively.Monosaccharide composition analysis was performed with the PMP-HPLC method.Date showed that EPS 1-1 was composed of Mannose,rhamnose,glucose,galactose and arabinose in a molar ratio of 0.05:0.21:0.05:0.06:1.EPS1-2 was composed of Mannose rhamnose,glucose,galactose and arabinose in a molar ratio of 0.08:0.24:0.04:0.09:1.EPS2-1 was composed of rhamnose and arabinose in a molar ratio of 0.43:1.And the infrared spectrum analysis results indicated that it is a polysaccharide.The method of ultrafiltration technique was adopted for separation of Auto-growth Inhibitors of Spirulina platensis.The effect of molecular weight cut offs(MWCOs)of membrane on removal efficiency was investigated.Ultrafiltration conditions for the Auto-growth Inhibitors of Spirulina platensis extracts from reused culture medium were optimized by orthogonal array design based on membrane flux.It is indicated that 100 kDa membrane can reduce Auto-growth Inhibitors effectly,and the optimized ultrafiltration conditions were found to be 0.20 MPa,450 r/min,35℃ and 9 for pressure,Mixing speed,temperature and sample pH,respectively.Finally,Membrane fouling and cleaning method were analyzed,the results show that main resistances for membrane fouling are gel layer,hole absorb and concentration polarization witch share 89 percent in total resistances.Membrane self and irreversible resistance share 29 percent and 11 percent each other witch occupy little.Thus the best method for membrane is washing the membrane with deionized water at 35℃ for 0.5h,and the flux recovery rate of membrane after cleaning was about 94%. |
